<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function factorial(n) {
            var s = 1
            for (var i = 1; i <= n; i ++) {
                s *= i
            }
            return s
        }

        const d = parseInt(prompt('请输入一个数'))
        var r = 0
        for (var j = 1; j <= d; j++) {
            r += factorial(j)
        }
        alert(r)
    </script>
</body>
</html>